1. Field of the Invention
The invention relates to a spectrophotometer and, more particularly, to a spectrophotometer having an improved specimen chamber.
2. Description of the Prior Art
In a spectrophotometer, especially one using visible and/or ultraviolet light beams, of the type in which a specimen chamber is provided for mounting a specimen cell, an optical system is designed so that an optical path of a measuring light beam crosses the specimen cell mounted in the specimen chamber, and the specimen chamber is provided with an opening through which a sample is mounted or dismounted to and from the specimen chamber, a cover plate is generally provided to cover the opening for shielding the specimen chamber from external light during measurement. This is because in the spectrophotometer using visible and/or ultraviolet light rays, the leakage of external light into the specimen chamber often causes measurement errors greater than tolerable limits. Therefore, it is necessary to seal the specimen chamber substantially completely from external light by covering the opening with the cover plate when the measurement is conducted. If the mounting and dismounting of samples to the specimen chamber are required repeatedly many times, the cover plate is also required to be opened and closed repeatedly many times. Therefore, the cover plate is desired to be supported by the spectrophotometer body even when it is opened, for convenience of its handling. In the conventional spectrophotometers of this type, therefore, the cover plate is pivotably mounted to one of the specimen chamber walls defining the opening, such that it is movable between an opening position where the specimen chamber is open and a closing position where the specimen chamber is closed. However, such spectrophotometers have various disadvantages. First, in order to completely seal the specimen chamber from external light at the pivotal coupling part using hinges, for instance, between the cover plate and the chamber wall, the structure of the coupling part is considerably complicated. Also, it is not easy to remove the cover plate from the chamber wall. Thus, in order to open the opening of the specimen chamber for changing sample cells, the cover plate must be rotated by more than 90.degree. from the closing position to the opening position. After change of the specimens, the cover plate must be returned to the closing position again. When many samples are measured but the time required for measuring each sample is relatively short, the cover plate must be opened and closed frequently in a short time. Therefore, such a large motion required for each opening or closing of the cover plate is troublesome for an operator, and it is disadvantageous that a large space is necessary for allowing such a large motion of the cover plate. In addition, the spectrophotometer is usually provided with a pen-write recorder on one side of the specimen chamber, and the recording paper moves over a part of the specimen chamber. Accordingly, the recording paper is obstructive to the opening and closing of the cover plate. This makes the opening and closing operations more troublesome. A high performance spectrometer generally has various attachments such as a rotating cell holder, a flow cell device, a thermostat cell holder, an integrating sphere which are selectively mounted in the specimen chamber when conducting specific measurements. Some of the attachments are large in size and prevent, when mounted in the chamber, the cover plate from being closed. Therefore, the measurement using such attachments must be done by shielding the chamber from external light with a suitable material other than the cover plate, while it is held at the opening position. However, this is also troublesome, because the cover plate located at the opening position is obstructive of the measures for light-shielding.